System and method for detecting lubricant in the fuel of an internal combustion engine

ABSTRACT

A system for an internal combustion engine ( 10 ) arranged for being powered with a fuel mixed with a lubricant, which system includes:—a detector ( 16 ) arranged for detecting the presence of a given additive in the lubricant mixed fuel—an electronic module ( 24 ) arranged for comparing the detected presence of the additive with a predetermined threshold value, and designed so that if the lubricant is not mixed in the fuel, or has been mixed in the fuel in an amount lower than a through the additive against the threshold value correlated amount, by means of an indicator ( 30 ) indicate that a lack of lubricant is at hand in the fuel and/or by means of a connection ( 26 ) to an ignition or injection system ( 11 ) for the engine ( 10 ) prevent or modify the operation of the internal combustion engine if said lack of lubricant is at hand in the fuel. The invention also refers to the method of how the system operates.

This application claims the benefit of International Application NumberPCT/SE03/00563, which was published in English on Oct. 23, 2003.

TECHNICAL FIELD

The invention refers to a system and a method for an internal combustionengine arranged to be operating on a mixture of fuel and lubricant, i.e.typically a two-cycle engine.

BACKGROUND OF THE INVENTION

Most two-cycle engines and even some recently developed four-cycleengines require a continuous supply of lubricant. In such internalcombustion engines the lubricant is supplied continuously either bypumping small amounts of for example oil through a separate lubricationsystem to the vital parts of the engine or by mixing the lubricant inthe fuel at the time of refueling the fuel tank for said engine.

Different systems have previously been developed to avoid that, forexample two-cycle engines, sustain damage due to that the necessarylubricant for the engine is not present. These systems are typicallydesigned as part of a separate lubrication system, including a separatelubricant tank, whereas the presence of lubricant is indicated by thesystem, e.g. by means of a float device etc. connected to a gauge or aindicator lamp or directly to the ignition system for the engine.

In some engine applications it has proven to be impractical to use aseparate lubricant tank and/or a pump system to continuously supply thelubricant. Examples are hand held small two-cycle engines, used amongothers in chain saws, grass trimmers and cut-off saws, that are used invarying running conditions and thus the separate lubrication systemshave not been successfully applied. Due to the impracticality of theseparate lubrication systems the lubricant is usually added/mixed to thefuel before the fuel is filled into the fuel tank of the engine.

One problem of supplying the lubricant to the engine through supplytogether with the fuel is to detect if a lubricant is present in thefuel or not. It is however common that a lubricant that is intended tobe mixed in fuel is distinctly colored by, for example, a blue, green orred die. When said colored lubricant is mixed in the fuel the mixture oflubricant and fuel will also be fairly strong colored and can thusvisually be inspected in for example a transparent vessel. Such aninspection is however dependent on that the operator is aware of theproblem and that he actively takes the measures to check if lubricanthas been added to the fuel. There is therefore nothing that prevents anengine from being operated even though an improper mixture offuel/lubricant is used.

The result of operating an internal combustion engine that requires acontinuous supply of lubricant without lubrication is usuallysignificant engine damage before the operator gets any indication ofthat the lubricant is not present.

SUMMARY OF THE INVENTION

It is the general object of the invention to provide a system and methodthat prevents or at least minimizes the problems outlined above.

More specifically the invention intends to present a system and a methodthat gives an indication/warning and/or prevents or changes theoperation of an internal combustion engine whenever no or aninsufficient amount of lubricant is present in the fuel.

These and other objectives are achieved with the system and method ofthe invention as presented in the patent claims

The invention idea is based on an automatic detection of the presence oflubricant in the fuel, that the detected amount of lubricant is comparedto a predetermined threshold amount and that an indication is given whena lack of lubricant is detected, i.e. when the threshold amount is notreached and/or that the engine operation is prevented or altered when alack of lubricant is at hand. Change of the operation of the engine ispreferably arranged so that only an idle speed is allowed if a lack oflubricant is detected in the fuel. Normally, engine damage will notoccur if the engine operates at an idle speed or at a low RPM sinceresidual lubricant normally remains from previous operation and is notwashed away directly.

It has however been established that it is difficult to directly detectif a proper amount of lubricant is present in the fuel/lubricant mix,thus according to the invention an additive is used that enablesdetection. It is therefore the presence of this additive that isdetected and the pre determined threshold amounts is for the presence ofthis additive. The presence of lubricant is however directly correlatedto the presence of the additive since the additive is mixed into thefuel in an amount in direct proportion to the amount of lubricant.Preferably the additive is mixed directly into the lubricant alreadybefore the sale of the lubricant but it is also feasible to mix theadditive and lubricant separately in the fuel.

The threshold amount can preferably be adjustable whereas it iscalculated and adjusted with consideration to the type of additive andlimits of the mixing ratio between the fuel, lubricant and additive. Thethreshold amount is thus dependent on how much additive that is mixedinto the mix of lubricant and fuel and what the lower limit for themixing ratio between lubricant and fuel should be—typically minimum0.5%, preferably minimum of 1% lubricant in the fuel. In one embodimentof the invention an upper threshold amount could be utilized,correlating to an upper limit for the mixing ratio between the lubricantand the fuel, typically maximum 0.5% or preferably maximum 1% lubricantin the oil. When this upper threshold amount is exceeded the system canindicate this in a different way from the case when the lower limit isreached, whereas however normally the engine operation does not need tobe actively prevented or altered. At given limits and a known additivein a known concentration the threshold amount can be fixed i.e. does notneed to be adjustable.

In a first embodiment of the invention the additive used is changing,preferably increasing, an electrical conductivity or capacitance of themixture of fuel and lubricant, whereas the detection of the additive inthe lubricant/fuel mixed fuel is arranged in terms of a conductivity orcapacitance and said threshold amount is a threshold amount in terms ofconductivity or capacitance.

In accordance to a second embodiment of the invention said additive isan additive that changes an optical property of the mixture of fuel andlubricant. The detection of the presence of the additive in thelubricant mixed fuel, is arranged in terms of this optical property andsaid threshold amount is a threshold amount expressed in terms of thisoptical property. Preferably an optic-electronic detector is used forthe detection of the additive, such as a light emitting diode (LED) anda photo transistor, whereas the additive is a dye adapted to absorblight of the same wavelength as emitted by the LED. It is however alsopossible to use any other source of light and light detector, i.e. inany wavelength or spectrum whereas the additive is adapted for theselected wavelength or spectrum.

DESCRIPTION OF THE DRAWING

The invention will be described in more detail in the following withreference to FIG. 1 that is schematically illustrating a systemaccording to the preferred second embodiment of the invention.

Item number 10 and 11 in the system in FIG. 1 symbolize a two-cycleinternal combustion engine and its ignition system. A fuel tank 12 isconnected to the engine 10 with a fuel line 14. The fuel tank is filledwith a fuel, normally gasoline, together with a lubricant, normally oil,and an additive to be detected, in predetermined proportions. Theadditive is in this embodiment of the invention a colorant (dye) thathave light blocking characteristics in a selected wave length spectrumof for example 400 to 450 nanometer (nm) i.e. blue visible light. Evenother dyes that have light blocking characteristics in any other wavelength spectrum, for example the infrared spectrum at about 900 nm couldbe used.

The fuel line 14 has a transparent part at a detector 16. The detector16 includes in this preferred embodiment a light emitting diode(LED) 18and a photo transistor 20. The LED 18 is selected and adapted to emitlight within the same wave length spectrum as the spectrum at which thedye has light blocking properties. When a mixture of fuel lubricant andadditive, i.e. dye, in the fuel line 14 is passing at the detector 16the light is blocked or weakened from the LED due to the dye. Thephototransistor 20 registers this blocking or weakening of the light andsends a signal through the electric wire 22, to a electronic module 24.In the electronic module the signal is compared to a predeterminedthreshold value for the dye concentration and thus an indirect detectionis made if the lubricant concentration is adequate, which it is if thethreshold value is exceeded.

If the threshold value is exceeded the electronic module indicates thatthis condition is fulfilled and the engine 10 is allowed to operate asnormal. On the other hand if the signal indicates that the value fallsbelow the threshold value, i.e. that a sufficient blocking or weakeningof the light from the LED 18 is not registered, the electronic module 24sends instructions to the engines 10 ignition system 11 through aconnection 26 to interrupt the ignition for the engine 10 or to only letthe ignition function properly at a low speed or at the idle speed. Thismeans that the ignition will turn on and off dependent of the speed ofthe engine, which gives a very specific operation of the engine. Thisalso means that the operator would not mistake the situation with anyother failures such as a faulty ignition. As an alternative or incombination with the electronic module 24 can send a signal to anindicator 30, for example a light or sound indicator, that is activatedwhereas the operator is made aware of the situation of a lack oflubrication. According to an aspect of the invention one could alsoimagine that the indicator 30 indicates the current concentration oflubricant on a display and even the amount needed to be filled in thefuel tank 12.

It is realized that the detector 16 and the threshold value can beadjusted to the colorants that according to the above already exists insome lubricants/oils today, with respect to the type of colorant ( i.e.what wavelength spectrum that they block) as well as its concentrationin the lubricant. As an alternative the detector 16 and its thresholdvalue is adjusted to a dye or additive specifically developed for thepurpose. Preferably such dye or additive would be mixed into thelubricant preferably already before the sale of the lubricant, but it isalso possible to mix the dye or additive and lubricant separately intothe fuel. With suitably selected dyes, for example one that blocks thelight in the wavelength spectrum of 400 to 450 nm it would be enoughwith as little as 2%, preferably less than 1%, and even more preferredless than 0.5% colorant in the lubricant. Not limited to such examplesof colorants are solvent based, oil soluble dyes including one or moreazo colorants. In connection with the development of the invention amongothers Liquid Yellow DRHF, Yellow GRHF, Yellow F2HF that aremanufactured by United Color Manufacturing, were used with success.These colorants include a mixture of monoazo and diazo colorants and allhave strong light blocking characteristics in the wavelengths of 400 to450 nm.

In the first embodiment of the invention the system is the same as thatillustrated in FIG. 1, with the exception that the detector 16 isinstead comprising two electrodes 18, 20 that are designed to detectelectrical conductivity in the lubricant mixed fuel. The electrodes arethen in direct contact with the lubricant mixed fuel whereas thetransparent part of the fuel line 14 is not needed. The additive in thiscase could consist of a component, for example an alcohol, that changes,preferably increases, the electrical conductivity or capacitance in themixture of lubricant and fuel, whereas the threshold value is expressedin terms of electrical conductivity or capacitance. Pure gasoline has avery low electrical conductivity or capacitance and this is also thecase for conventional lubricants, thus an additive would be required forthe detection.

According to one aspect of the invention the system could be designed sonecessary equipment such as detector, electronic module, etc. could beadopted to an already existing engine.

EXAMPLE

A cut-off saw was equipped with a system according to the invention asfollows.

A measuring bridge comprising a blue LED with a wave length of 430 nmand a conventional phototransistor were placed on opposite sides of aclear plastic tube with an inside diameter of approximately 6 mm. Theplastic tube was connected to the fuel line of the engine. The measuringbridge was connected to and powered by an electronic module.

The power source for the electronic module and the LED consisted of asimple inductive coil that was installed by the flywheel (with permanentmagnets) on a gasoline powered cut-off saw.

The ignition system of the cut-off saw has a simple grounding wire (killswitch wire) that is normally connected to a simple switch. When thekill switch wire is grounded at the switch by manually switching thesame, the ignition for the engine is shut off. On the prototype theground wire for the ignition was connected to the electronic module. Theelectronic module was then connected to the switch. For safety reasonsit should still be possible to switch off the ignition to the engineregardless of if the electronic module works or not.

The electronic module used on the prototype had the following functionsincluded:

-   -   1. The inductive coil at the flywheel is generating a low        alternating current of approximately 12 to 30 volts dependent on        the speed of the engine. The current is rectified and modulated        to power other functions of the electronic circuit and provides        the energy for the LED.    -   2. If the light from the LED does not reach the phototransistor        at a specific intensity (inverted threshold value) i.e. the        light is blocked by the colorant mixed in the oil/fuel mixture,        the engine will operate normally and it can also be shut off        with the switch in a normal fashion.    -    If the light from the LED reaches the phototransistor with a        higher intensity (exceeds the inverted threshold value or in        other words is lower than the threshold value) the        phototransistor gives off a higher current. The increased        current from the phototransistor is switching an electronic        switch for the ground wire from the ignition system to ground        thus no spark is generated as would be the case when a        mechanical switch is grounding the ignition system.    -   3. Since it is not desirable to turn off the ignition in the        same manner as with a mechanical switch yet another function was        included in the circuit which is that the ignition is only        turned off if the engine speed exceeds 4000 to 5000 RPM. Normal        idle speed for this type of engine is about 2000 to 3000 RPM.        This means that the engine can be started and operated at an        idle speed, but if the engine speed is increased past the 4000        to 5000 RPM the ignition is turned off. This results in a        decreased RPM whereas the ignition is again turned on. In other        words a very distinct engine operation is achieved that would        not be mistaken for any other types of known failure symptoms.    -   4. The threshold values for the blocking of the light and for        the engine RPM at which it is desirable for the ignition to turn        off was adjustable on the prototype. In a commercial application        it would be desirable that these threshold values would be        fixed. It would also be possible for them to be manually        adjustable and/or electronically controlled from other engine        functions in more sophisticated control systems.

The invention is not limited to the described embodiments but could bevaried within the scope of the patent claims. The skilled man thereforehas no problems to realize that the detector could for example be placedin a different place in the fuel system. As an alternative to a LEDanother light source could be used, for example a laser. It is alsoconceivable that the system and the method according to the inventioncould be used in connection with internal combustion engines that arepowered by a fuel mixed with lubricant, but where the lubricant isprovided directly to the engine from a separate lubricant tank and via apump system. Primarily the system is developed for small two-cycleengines that among others is used for chain saws, grass trimmers, andcut-off saws but could be utilized in all internal combustion enginesthat utilize a lubrication mixed fuel. The system and method if furthersuitable for engines that are spark ignited (S.I.) as well ascompression ignited (C.I.), whereas the system can not only be utilizedwithin the framework of an ignition system but also be connected to aninjection system, in a way that for example, the injection system isturned off or limited, if a threshold value is underpassed.

1. A system for an internal combustion engine (10) designed to be operated with a fuel mixed with a lubricant characterized in that it comprises: a detector (16) arranged to detect the presence of a specific additive in the lubricant mixed fuel, an electronic module (24) arranged to compare the detected presence of an additive with a given threshold value and designed so that; if the lubricant has not been mixed in the fuel or is mixed into the fuel, in an amount that is lower than an, via the additive against the threshold value correlated, amount, by means of an indicator (30) indicate a lack of lubricant in the fuel and/or with a connection (26) to an ignition system or an injection system (11) for the engine (10) prevent or change the operation of the internal combustion engine if such lack of lubricant is at hand in the fuel.
 2. A system according to claim 1, characterized in that said threshold value is adjustable for a correlation against the type of additive and the limits for a mixing ratio between fuel, lubricant and additive.
 3. a system according to claim 1 or 2, characterized in that said electronic module (24) via said connection (26) to the ignition system (11) of the internal combustion engine (10), is arranged to limit the speed (RPM) of the engine, preferably to only allow an idle speed, if a lack of lubricant is at hand in the fuel.
 4. A system according to claims 1 or 2, characterized in that said additive is an additive that changes, preferably increases, an electric conductivity or capacitance of a mixture of fuel and lubricant whereas said detector (16) is designed to detect the presence of the given additive in the lubricant mixed fuel in terms of electric conductivity or capacitance and whereas said threshold value is a threshold value for conductivity or capacitance.
 5. A system according to claim 4, characterized in that said detector (16) comprises two electrodes for the measurement of conductivity and capacitance.
 6. A system according to claim 1, characterized in that said additive is an additive that changes an optical property in the mixture of fuel and lubricant, whereas said detector (16) is designed to detect the presence of a given additive in the lubricant mixed fuel in terms of this optical property and whereas said threshold value is a threshold value in terms of this optical property.
 7. A system in accordance to claim 6, characterized in that said detector comprises an optical sensor, preferably in the form of a light emitting diode (18) and a phototransistor (20) whereas the said additive is a colorant adapted to absorb light in the wavelength or spectrum of the light emitting diode.
 8. A method relating to the operation of an internal combustion engine (10) that is powered by a fuel mixed with a lubricant, characterized in that; a presence of a given additive in the lubricant mixed fuel is detected (16) The detected presence of the additive is compared (24) with a set threshold value, whereas it, when the lubricant is not mixed in the fuel or has been mixed into the fuel in an amount lower than one through the additive against the threshold value correlated amount, indicates (30) that a lack of lubricant is at hand in the fuel and/or whereas the internal combustion engine operation is prevented or changed if said lack of lubricant is at hand in the fuel.
 9. A method according to claim 8, characterized in that said threshold value is adjustable for correlation against the type of additive, and the limits for a mixing ratio between the fuel, lubricant and additive.
 10. A method according to claim 8 or 9, characterized in that the RPM of the engine (10) is limited (26) preferably that only the idle speed is allowed, if a lack of lubricant is at hand in the fuel.
 11. A method according to claim 8, characterized in that said additive is an additive that modifies, preferably increases, an electric conductivity or capacitance of the mixture of fuel and lubricant whereas the detection (16) of the presence of said additive in the lubricant mixed fuel is measured in terms of electrical conductivity or capacitance and whereas said threshold value is a threshold value in terms of electrical conductivity or capacitance.
 12. A method according to claim 8, characterized in that said additive is an additive that changes an optical property of a mixture of fuel and lubricant, whereas the detection (16) of the presence of the said additive in the lubricant mixed fuel is measured in terms of this optical property and whereas said threshold value is a threshold value in terms of this optical property. 